Using nitride-based III-V group compound semiconductors such as gallium nitride (GaN), there have been developed semiconductor light emitting devices such as high-intensity ultraviolet to blue and green light emitting diodes (LED) and blue-violet to blue and green laser diodes (LD).
In order to provide an LED with higher efficiency, it is important to enhance internal quantum efficiency of a crystal by improving crystallinity of a GaN-based semiconductor.
Since a GaN-based semiconductor and sapphire used as a substrate have extremely high refractivity, multiple reflections occur inside a chip of a semiconductor light emitting device. As a result, low light extraction efficiency is likely to be obtained.
JP-A 2007-123878 (Kokai) proposes a configuration in which an energy band gap of a quantum well layer adjacent to an n-type nitride semiconductor layer is set to be larger than that of a quantum well layer adjacent to a p-type nitride semiconductor layer, with a view to improving internal quantum efficiency and luminance and decreasing an operating voltage.
However, this technique still has room for improving the efficiency.